Cell surface membranes are to be studied with serological and physical techniques. Diffusion of antigens in the plane of the membrane will be examined by three different techniques. Modification of membrane lipids will be performed and the diffusion rates for H-2 antigens will be correlated with physical changes measured by ESR and fluorescence methods. Antigen expression will be monitored in normal differentiating systems, and correlated with physical changes in membrane structure, such as changes in membrane viscosity. H-2 and tumor antigen expression will also be measured in deliberately modified cell membranes. Studies of the binding of labelled hormones to cell surfaces, as well as on the isolation of hormone receptors, will be continued in an effort to determine the effect of genes linked to the major histocompatibility complex on cell responses to polypeptide hormones.